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Do heart murmur grades tell you if a dog is in heart failure?

There are common misconceptions about heart murmurs that persist. Here are some links, and I could have listed many more. I’ve included some quotes from each site, and some comments of my own at the end.

“Although listening to the heart for abnormal heart sounds such as murmurs or gallops is an important way to look for heart disease, this only gives you an indication that the animal may have underlying heart disease. It doesn’t necessarily tell you which type of heart disease or how severe it is.

“Based on the type of abnormal heart sound, the location and the breed of animal, your veterinarian can often make an educated guess as to what type of heart disease your pet has based on what’s most likely, but this is still not definitive.”

Very technical site written by board certified cardiologist:
Cardiac Auscultation 101
Terri DeFrancesco, DVM, DACVIM (Cardiology), DACVECC
Associate Professor in Cardiology and Critical Care
NC State University College of Veterinary Medicine

“Veterinarians rank the intensity or loudness of a heart murmur in grades from one to six, with one being barely audible and six being the loudest. There is also a one-to-five ranking system that works the same way. These grades do not necessarily correlate with the severity of the heart condition; they are merely one of several ways that veterinarians attempt to characterize the murmur.”

Comments from Pat – There are cases where a murmur can actually become softer as the heart disease worsens. This is because the heart becomes increasingly enlarged so that there is less turbulence from regurgitant blood flow and thus less noise. Remember that a heart murmur is just a noise – it can give clues about the underlying disease and severity, but it is not diagnostic for heart failure. If it were, we wouldn’t need to do radiographs, electrocardiograms and echocardiograms in order to stage heart disease (along with considering the presence or absence of symptoms). My 16 year old shih tzu was diagnosed with heart failure a few weeks ago, and she has NO heart murmur at all. Radiographs showed an enlarged heart and pulmonary edema. She also had symptoms of labored breathing. The absence of a murmur was confirmed by two GP vets, an ER critical care specialist, and a cardiologist. This is unusual, but it is possible. (This is also a reason to get baseline chest radiographs on elderly dogs with no murmurs.)

The point is that you CANNOT diagnose the severity of underlying heart disease or whether a dog is in heart failure based on the grade of a murmur. Similarly, no vet should decide whether to prescribe meds or not based only on the grade of a murmur. A murmur is simply a noise that gives you a notice to monitor and do appropriate follow up and testing.

In addition to Pat's information, and just anecdotally, a grade 6 murmur has been known to change to a grade 5 as the heart continues to enlarge, due in part to fluid build-up which inhibits transmission of the sound of the back-flowing blood. So, it is possible that the MVD worsens but the murmur intensity lessens.

Great info it makes sense to me. So an abnormal heart sound or murmur is one indication or symptom of a heart not working properly not really heart failure. However, there are other symptoms like labored breathing and weakness. I knew that heart murmurs could change for a number of reasons. My son had a "small murmur" at birth however after some testing they told me he should outgrow it which he did. We still do every other year EKG's because of that AND the medicines he takes (we also do annual bloodwork). I was wondering that knowing all we do about MVD is it a good idea to take a cavalier to a cardio for a workup? Knowing almost all will have this heart problem? Is that being overly careful? And if not and you advice it why? Ok, it might be good to know you dog has symptoms or a murmur but what would a owner do differently? There is no treatment for the symptoms right? Do you think striving for a heart heath in cavaliers is making any difference? I would think a dog who develops a heart abnormality with a good healthy strong heart might fair better than a dog who was overweight and unfit. Or again is that the crazy in me talking? I think the best thing to do at this point is to do my best to make sure Fletcher's heart is as healthy as it can be. Educate myself about MVD (and all the other things medically that might be likely to develop) and be watchful. Anyway, I appreciate your explanation and links.

Melissa
"If you don't own a dog, at least one, there is not necessarily anything wrong with you, but there may be something wrong with your life."
-Roger Caras

... I was wondering that knowing all we do about MVD is it a good idea to take a cavalier to a cardio for a workup? Knowing almost all will have this heart problem? Is that being overly careful? And if not and you advice it why?

I think that all cavaliers should be examined at least annually for a murmur, as that is the first indication of the onset of MVD. This examination is a simple one, using a stethoscope, but it is not easy, and therefore should be performed by a competent vet with some experience in detecting heart murmurs.

The best category of vet to do this would be a cardiologist, but anyone who has taken a dog to a cardiology clinic knows that a "work up" can be expensive, because it almost always includes not just the stethoscopic exam -- called "auscultation" -- but also an ultrasound exam. I don't think that an ultrasound normally is necessary when all we are trying to find out is if MVD has commenced.

As an aside, keep in mind that MVD consists of the mitral valve (one of four valves in the heart) failing to fully close when it should, causing some blood to backflow in the direction opposite to the intended flow of blood through that valve. So, using a stethoscope with its chestpiece placed over the area of the mitral valve, the vet listens for the murmur which would be produced if the valve was not closing fully and was allowing blood to flow in reverse through the valve.

So, a solution is to find a cardiologist who will just use his stethoscope (and not his expensive ultrasound machine). That often is easier than it may seem, because cardiologists often spend their Saturdays and/or Sundays at dog shows holding "heart clinics". In the US and Canada, dozens of these heart clinics are held throughout these countries throughout each year. There is a continually updated list of them at http://www.cavalierhealth.org/health_clinics.htm

And so, I recommend that owners take their cavaliers to one of these nearby heart clinics each year. If you cannot do that, then find a really good general practice veterinarian, from a really good vet school, who has had training in listening to heart valves and grading murmurs.

Now, if and when a vet first hears a murmur, he should grade it. Hopefully initially it will be a low grade, like a 1 or a 2. The next thing the owner should do is get an x-ray of the dog's heart. Since the main symptom of congestive heart failure is enlargement of the heart due to MVD, an early x-ray of the heart, at or before the onset of an MVD murmur, would be very helpful later on as the disease progresses.

At the onset of MVD -- a low grade murmur -- the average cavalier does not need to see a cardiologist for a full blown workup.

Originally Posted by MomObvious

... Ok, it might be good to know you dog has symptoms or a murmur but what would a owner do differently? There is no treatment for the symptoms right? Do you think striving for a heart heath in cavaliers is making any difference? I would think a dog who develops a heart abnormality with a good healthy strong heart might fair better than a dog who was overweight and unfit. Or again is that the crazy in me talking? I think the best thing to do at this point is to do my best to make sure Fletcher's heart is as healthy as it can be. ...

I think that keeping the cavalier's heart as healthy as possible is the proper course, even before onset of the low grade murmur. We add vitamins and supplements to our cavaliers' food. A list of various such additives are here: http://www.cavalierhealth.org/mitral...--_supplements

We think that supplements and vitamins have made a difference, but of course we cannot prove that from our dogs.

The current consensus for medicating MVD is to wait until the onset of congestive heart failure (CHF). This is because the current crop of drugs have not been shown to delay the onset of CHF.